Provide an in-app push helper for push notifications

[David Planella]

We need to add a push helper to set up and handle push notifications.

Raw notes from the discussion at the Washington sprint:

Register app with the push server (OAuth signer request) and the app server (POST) (it can be done every time the app starts) (check out hello-app http://bazaar.launchpad.net/~ubuntu-push-hackers/ubuntu-push/trunk/files/head:/docs/)
Token from the push server push.ubuntu.com/register (user id + token)
Examples:
- Telegram
- Facebook, GMail, Twitter webapps

Sample URL:
http://162.213.34.150:7778/evernote/v1/webhook?userId=verterok-test&notebookGUID=10

Endpoint for registering:
http://162.213.34.150:7778/register

The body of the POST request to register to the push-evernote-appserver is: {"userid": "<userid>", "token":"<atoken>", "appid": "<appid>"}
 curl -i -H "Content-Type: application/json" -X POST -d '{"appid": "com.ubuntu.reminders_reminders", "userid": "verterok-test", "token": "Yd3GITbQpewT9UwujEs+WA=="}' http://162.213.34.150:7778/register

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:reminders-app at revision 330, scheduled for release in reminders-app, milestone 2014-11-27